We have been running a late 80s 9.8 Mercury long shaft on a Jack's Daddy cat since the early 90s, usually tying a 14' SB on each side and towing a fourth. We finally got a second motor (2004 regular shaft Merc 9.
allowing more boats and even more importantly serving as reduancy in the event of problems with the older unit. Twice we have had carbueration/lower unit gear issues resulting in a long row out on Powell, with white-caps no less.
We use 6 gallon external tanks and additional plastic jugs and plan for 15 gal per motor for the day in on the Colorado and the next day out on the lake.
Frames are all home made from 1 1/4" and 1 1/2" EMT.
The longer shaft works best for us, just watch for sand bars and carry an extra prop.
Depending on the flow we either tilt and strap the motor in place, now the front of the CAT, or remove and secure onto frame as cargo.
Experience is best for shore-side repairs, and carry a good tool kit and extra prop and impeller for water pump. Removing the spark plug and lots of pulling will eventually clear water from a motor that has been on the flip-side.
2-strokes are lighter than 4-stroke, and the newer models are much quiter than the 80s version. Plywood or sheet metal bottoms on the motor frame help prevent water drag/splash and almost act as a planing hull when the boat is empty. Requires two people as ballast sitting close to the front to trim the motor.
Memorial day wind event caught us on the Colorado and near the loop the old motor was declared dead after a shore-line carbuerator re-build and we ended up towing 2 cats and two 14' SB rafts in a tight single line to break the wind and whitecaps. Front tow rig was a 16' Sotar cat and standing up to avoid the drowning spay the boat was launching more than half out of the water at times. Wind finally broke on our third day for the big drops and uncommon flat water on the lake. We are now in the market for another Mercury model (2004) 9.8 long-shaft two-stroke and plan to make a stern mount frame for the SBs.